Asynchronous transfer mode (ATM) is a connection oriented, cell based switching technique and is attracting a great deal of interest in the field of telecommunications. Networks based on the ATM switching technique promise flexible, high speed communication capability.
In existing telephone networks, new connection requests are blocked on the basis of a shortage of trunks. In an ATM node this is not the case since the physical resources are allocated virtually, and shared by many connections. However because the resources are shared, some limit must be placed on the number of simultaneous connections which are carried in order to maintain an acceptable quality of service.
Connection Admission Control (CAC) is the traffic control function of an ATM network, responsible for accepting and blocking calls to maintain an acceptable quality of service while maximizing network utilization. At call set-up a traffic contract is negotiated between the user and the network. The user declares a set of traffic descriptors (or equivalently a single traffic class descriptor) and a required quality-of-service (QOS). Based on these parameters and existing network load, the call may be accepted or rejected, usually based on a quality of service prediction.
Traffic from a number of calls is multiplexed together at a multiplexer or in a switch onto a single resource of capacity C bits per second (bps). This capacity might relate to a physical quantity such as a link capacity, or a virtual quantity such as a virtual path (VP) bandwidth allocation. Because the aggregate incoming traffic can exceed the outgoing capacity C, some of the traffic must be discarded resulting in cell loss. Among many indicators, e.g. cell delay, cell jitter etc., the cell loss is the most important QOS indicator with respect to connection admission. In order to make a connection admission decision some model of the system must be employed in order to derive a measure indicative of a predicted cell loss probability. The measure is based on traffic descriptors (parameters) for each call which the user declares at each call set-up. Burst traffic can be modelled as on-off traffic and described by three parameters; peak rate, mean rate and burst length. A measure based on the bufferless multiplexer model is simply calculated by two parameters of peak rate and mean rate which are easy for a user to declare and for the network to enforce. The control model of the present invention uses this simple bufferless multiplexer model. Use of this kind of model, both to represent ATM switching processes, and as a basis for connection admission, has been reported in recent literature. T. Murase, H. Suzuki, S. Sato, T. Takeuchi, "A call admission control scheme for ATM networks using a simple quality estimate", IEEE JSAC, vol. 9, no. 9, pp 1461-1470, December 1991, and C. Rasmussen, J. H. Sorenson, K. S. Kvols, S. B. Jacobsen, "Source independent call acceptance ATM networks", IEEE JSAC, vol 9, no. 3, pp 351-358, April 1991. However fast and accurate methods to solve this model have until this time been unreported.